This invention relates generally to devices for use with electrical monitoring systems, and more particularly to opto-isolation couplers for use therein and methods of such use.
As will be appreciated by those skilled in the art it is a common practice to utilize opto-isolation devices (also commonly referred to as optically coupled isolators) in electrical circuits to enable the monitoring of an electrical parameter of one circuit (or portion of a circuit) by another circuit (or portion of a circuit) while providing that the two circuits (or portions) are electrically isolated from each other. Thus, conventional opto-isolators effect such action by converting the electrical signal (.parameter) of the circuitry being monitored into a light signal representative thereof. The light signal is most commonly produced by an LED and is transmitted through a high dielectric strength, light-transmissive material, e.g., an air gap, fiber optic cable, etc., to a device, e.g., a photodetector, for converting the light received into an electrical output signal indicative thereof. The electrical output signal can then be provided to the monitoring circuitry for use thereby. An example of an LED-based opto-isolator is shown in U.S. Pat. No. 4,032,843 (Loucks).
While conventional LED-base opto-isolators are suitable for their intended purposes, they nevertheless leave much to be desired from the standpoint of electrical isolation (transparency) in high voltage applications. This is the direct result of the fact that conventional LED-based, opto-isolators require significant current, e.g., 10 milliamps, to produce sufficient light for reliable operation. Because of this characteristic if a LED-based, opto-isolation device is utilized in the monitoring of a high voltage circuit objectionable action could result. For example, if such an opto-isolator is connected in shunt with a limit switch in a high voltage circuit, e.g., a 480V boiler control circuit including the limit switch and a relay operated circuit breaker, to monitor the voltage across that switch when it opens, the flow of current through the opto-isolator's LED will result in an excessively large amount of power drawn, e.g., several watts. Moreover, depending upon how the boiler control circuit is arranged, the relatively high current, e.g., 10 milliamps, flowing through the opto-isolator could cause undesired operation of the circuit breaking relay after the event which triggered the opening of the limit switch.
The use of Neon or other glow-tube based opto-isolators has been disclosed in the following U.S. Pat. Nos.: 3,141,131 (McCoy), 3,991,367 (Chapman et al), 4,015,201 (Chaffee), and 4,188,574 (Allington).